The present invention is in the field of battery technology and, more particularly, in the area of using coatings to enhance electrolyte and electrode performance in batteries including metal-fluoride, carbon-fluoride, or oxide-based electrode materials.
One type of battery consists of a negative electrode made primarily from lithium and a positive electrode made primarily from a compound containing carbon and fluorine. During discharge, lithium ions and electrons are generated from oxidation of the negative electrode while fluoride ions and carbon are produced from reduction of the positive electrode. The generated fluoride ions react with lithium ions near the positive electrode to produce a compound containing lithium and fluorine, which may deposit at the positive electrode surface.
Lithium/carbon-fluoride batteries enjoy widespread use and commercial applicability in part due to certain desirable characteristics. The carbon-fluoride positive electrode is lightweight, which makes the battery desirable in portable or mobile applications where weight is an important design consideration. Also, the carbon-fluoride positive electrode has a high capacity. Further, the overall reaction has a high electrochemical potential.
Another type of battery consists of a negative electrode made primarily from lithium and a positive electrode made primarily from a compound containing metal oxides. During charge and discharge cycles, lithium ions migrate from one electrode to the other where the direction of migration depends on the cycle.
Despite their widespread use, both types of batteries suffer from certain challenges.
The batteries have comparatively low electrical and ionic conductivity as compared to certain other battery materials. Such comparatively low electrical and ionic conductivity can have the following results in an electrochemical cell: comparatively low power; comparatively low operating voltage; comparatively large underpotential upon discharge; and a comparatively low capacity during a high rate of discharge.
The batteries have comparatively low thermal conductivity as compared to certain other battery materials and such comparatively low thermal conductivity can result in comparatively significant heat generation by the electrochemical cell upon discharge.
There have been prior attempts to address such challenges. One prior attempt involves forming a composite positive electrode. The raw composite material contains a carbon-fluoride compound and a second compound, which is comparatively more electrically conductive than the carbon-fluoride compound. These two compounds are mixed together to form a composite material that is then formed into a positive electrode.
One example of such a composite material is a carbon-fluoride compound composited with silver vanadium oxide (silver vanadium oxide is often abbreviated as “SVO” in the battery industry rather than by its periodic table symbols). This CF/SVO composite material has been used to form a positive electrode in a battery for use in medical devices and has demonstrated increased pulse power and increased energy density when compared to a battery using a positive electrode formed only from carbon-fluoride.
Another example of a composite material for use in forming a positive electrode is a carbon-fluoride compound composited with manganese dioxide (MnO2). This CF/MnO2 composite material has been used to form a positive electrode where cost is a key design factor and has demonstrated increased power at high discharge rates, increased energy density, and reduced heat buildup in the electrochemical cell when compared to a battery using a positive electrode formed only from carbon-fluoride.
Although prior batteries using positive electrodes formed from these and certain other composite materials generally have higher power, higher operating potential, lower underpotential, and less heat buildup when compared to batteries using a positive electrode formed only from metal-fluoride or carbon-fluoride, the performance of the electrochemical cell could be improved significantly. Also, certain of these performance improvements come at the expense of reduced energy density.
In some prior batteries, conductive coatings have been applied to electrode materials. In secondary battery applications, some electrodes have been formed from carbon-coated LiFePO4. Also, some research has occurred on coating carbon-fluoride compounds used for electrodes in primary batteries (see Q. Zhang, et al., Journal of Power Sources 195 (2010) 2914-2917). Prior art coatings are typically applied at high temperatures and under inert atmosphere which can degrade cathode active materials. Thus, temperature-sensitive active materials for cathodes have not typically been coated with conductive carbon materials.
Certain embodiments of the present invention address the challenges found in batteries. Certain embodiments of the present invention can be used to form electrochemical cells for batteries that exhibit lower underpotential, higher power, higher capacity at a high discharge rate, less heat generation, or faster heat dissipation when compared to prior batteries.
These and other challenges can be addressed by embodiments of the present invention described below.